This invention relates to a nuclear power plant containment system and in particular to a molten core retention and solidification apparatus that removes heat from a molten core within the containment building while preventing the molten core from penetrating the base of the containment building.
When the core of a nuclear reactor produces more heat than is removed from the core for a sufficiently long time period, the temperature of the core will rise and eventually exceed the melting temperature of its constituent materials. The core will melt through the reactor vessel and fall onto the structure beneath the reactor vessel. Core retention devices are designed to prevent the molten core and molten reactor vessel from penetrating the base of the containment building of a nuclear power plant. The various prior art core retention concepts fall generally within four categories. These categories are water heat sink, sacrificial bed, crucible, and mass dispersal.
The water heat sink core retention concept provides a large reservoir of water beneath the reactor vessel into which the molten core or molten reactor vessel falls. Heat is removed from the molten core as the temperature of the water increases and as water changes state to form steam. This core retention concept requires a large cavity beneath the reactor vessel to retain the reservoir of water. Furthermore as the water changes state to steam, makeup water must be provided and the steam produced pressurizes the containment building.
The sacrificial bed core retention concept contains a bed of material beneath the reactor vessel that is sacrificed as the molten core is deposited on the bed. The bed may be miscible, where the bed dilutes the molten core or immiscible, where the molten core floats on top of the bed. The sacrificial bed may also be of a solid material, such as lead, that vaporizes when the molten core is deposited on the sacrificial bed.
The crucible core retention concept places a large crucible beneath the reactor vessel. The crucible can take the thermal and mechanical loads of a melting core or reactor vessel and simply catches and holds the molten material.
The mass dispersal core retention concept disperses the molten core or reactor vessel throughout a large heat sink contained beneath the reactor vessel.
Prior art core retention concepts attempt to contain within the containment building both the molten core or reactor vessel and the energy contained within the molten core or reactor vessel. Retaining the molten core or reactor vessel within the containment building is essential. However, it is not necessary to contain the heat energy content of the molten core or reactor vessel within the containment building.
Therefore, a need exists for a heat exchanger molten core retention and solification apparatus to contain the mass of the molten core or reactor vessel while simultaneously removing the heat content of the molten mass from within the containment building.